1. Field of the Invention
The present invention relates to a chroma noise reduction device for eliminating noise components from a chroma signal of a television, VTR, etc., and, in more particular, a chroma noise reduction device for automatically adjusting the phase and amplitude of a delay signal obtained from an 1H delay element, such as a CDD, etc.
2. Description of the Related Art
Conventionally, a chroma noise reduction device for television, VTR, etc., is as shown, for example, in FIG. 1. In FIG. 1, a chroma signal vi supplied from a final stage of a chroma circuit is fed to one input terminal of each of a subtracter 11 and adder 12. The output of the subtracter 11 is supplied to a CCD 13 serving as a 1H delay circuit for delaying the signal by a 1 horizontal period. The 1H delay signal from CCD 13 is supplied to a variable amplifier 16 through a filter circuit 14 and variable delay unit 15, the filter circuit 14 being used to delay a clock signal, etc., contained in the output signal of CCD 13. An output signal V.sub.2 of the variable amplifier 16 is fed back to the other input terminal of the adder 12. The adder 12 adds together the input signal V.sub.i and one horizontal period-prior signal V.sub.2 which is output from the variable amplifier 16. A result of addition is supplied to the other input terminal of the subtracter 11 through a limiter 17 for amplitude limitation. The output signal of the limiter 17 is subtracted from the input signal V.sub.i by virtue of the subtracter and the output signal V.sub.0 is supplied to an YC addition circuit, not shown, and to CCD 13.
CCD 13, filter circuit 14, variable delay unit 15 and variable amplifier 16 constitute external component parts. The variable delay unit 15 and variable amplifier 16 are manually adjustable, by an operation of a volume, at the phase and amplitude of the 1H delay signal.
In the arrangement above, it is necessary that, in order to obtain a desired characteristic, exact matching be achieved in amplitude and phase between the input signal V.sub.i and the 1H delay signal. Conventionally, the phase delay time of the variable delay unit 15 and amplitude of the variable amplifier 16 had been adjusted while monitoring the output signal of the adder 12.
In the chroma noise reduction device thus arranged, however, more external component parts and more manufacturing steps and more occupation areas are required upon the manufacture of a printed circuit board, etc. Further, the manufacturing cost is also higher. Since, during the portion of the manufacturing process, the operator has to manually adjust the variable delay unit 15 and variable amplifier 16 while monitoring the output signal of the adder 12, it becomes cumbersome to make adjustment and a high cost results from this viewpoint. In addition, the phase delay time of the variable delay unit 15 and amplitude of the variable amplifier 16 are also fixed after adjustment has been achieved, making it difficult to cope with a time variation and aging.